Some designs of mobile communication devices—such as smart phones, tablet computers, and laptop computers—contain one or more Subscriber Identity Module (SIM) cards that provide users with access to multiple separate mobile telephony networks. Examples of mobile telephony networks include Third Generation (3G), Fourth Generation (4G), Long Term Evolution (LTE), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), Wideband CDMA (WCDMA), Global System for Mobile Communications (GSM), and Universal Mobile Telecommunications Systems (UMTS). A mobile communication device that includes one or more SIMs and connects to two or more separate mobile telephony networks using one or more shared radio frequency (RF) resources/radios is termed a multi-SIM mobile communication device. One example is a multi-SIM-multi-standby (MSMS) communication device, which includes two or more SIM cards/subscriptions that are each associated with a separate radio access technology (RAT), and the separate RATs share one RF chain to communicate with two or more separate mobile telephony networks on behalf of each RAT's respective subscription.
When none of the RATs, or subscriptions supported by the RATs, in a multi-SIM mobile communication device is actively communicating with a network, each subscription enters idle mode. In the idle mode, a subscription repeats a discontinuous reception (DRx) cycle, each cycle lasting for a predetermined amount of time. During each DRx cycle, the subscription is not communicating with the network. At the end of each cycle, the subscription performs an idle mode wakeup, which means the subscription temporarily resumes contact with the network to receive network information before beginning the next DRx cycle. This network information is used to perform idle mode operations that allow the subscription to remain synchronized with the network. The network information obtained from the network may include, but is not limited to, system information blocks, sample RAM values, and neighbor cell measurements. Idle mode operations may include, but are not limited to, reception automatic gain control computations, cell reacquisition operations, finger triage operations, quick finger tracking or quick time tracking operations, equalizer weight computations, page indicator channel monitoring operations, selection criteria and reselection criteria evaluations, inter- and intra-frequency neighbor measurements, decoding of system information blocks, antenna switch diversity algorithms, and idle diversity operations. For a multi-SIM mobile communication device in which all subscriptions are in the idle mode, each subscription performs an idle mode wakeup to acquire network information from each subscription's respective network, and performs idle mode operations using the acquired network information.
When one subscription is used to make a voice call, for example a circuit switched call, the subscription leaves idle mode and enters an active mode in which the subscription is in communication with a network. While one subscription is in the active mode the other subscriptions remain in the idle mode. Because a voice call has a higher priority than an idle mode wakeup, the idle subscriptions cannot interrupt the voice call to perform an idle mode wakeup with each subscription's respective network through the shared RF resource. This may result in the idle subscriptions going into out-of-service status as the idle subscriptions are no longer synchronized with each subscription's respective network. Once the voice call ends, each of the idle subscriptions may undergo a full network search to reconnect with each subscription's respective network. This full network search may consume a large amount of device resources and power, and may take a relatively long time to perform.
In another situation, one subscription may leave idle mode to engage in active data communication with a network while the other subscriptions remain in the idle mode. However, the idle subscriptions may periodically interrupt the active subscription's data communication to perform idle mode wakeup using the shared RF resource. This process of switching access of the shared RF resource from an active subscription to an idle subscription is sometimes referred to as a “tune-away” because the RF resource tunes away from the active subscription's frequency band or channel and tunes to the idle subscription's frequency bands or channels. After the idle subscription has finished network communications during the idle mode wakeup, access to the RF resource may switch from the idle subscription to the active subscription via a “tune-back” operation. A tune-away interrupts the active subscription's data communication, which may result in the loss or degradation of data.
For multi-SIM mobile communication devices, more than one subscription may sometimes be connected to the same network operator and the subscriptions may connect to the same base station used by the network operator. In this situation, the network information that is received from the network during idle mode wakeup is the same for all subscriptions that share the same network operator and base station. In addition, because idle mode operations are conducted using the network information, the results of the idle mode operations may be the same for all subscriptions. However, because each subscription conducts idle mode wakeup and idle mode operations independently, there may be duplicative communications with the network base station and duplicative performance of idle mode operations. The independent idle mode activities of each subscription may collectively consume a large amount of device resource and power. In addition, problems arise when the idle mode activities of idle subscriptions interfere with an active subscription in a voice call (out-of-service status for idle subscriptions) or in data communication (tune-aways to the idle subscriptions degrade data communication).